json config reader in C-CodePudding

I have this config data in this json,

{
    "difficulty":-1,
    "damage":100,
    "infinite":true,
    "tilewidth":16,
    "type":"map",
    "version":"1.2.4"
}

and i want to store these variables in my program.I cant use a Map cause there isn't a fixed type to read (int,string,bool)...

using JSON = nlohmann::json;
/* struct Configs final {
  int difficulty;
  int damage;
  bool infinite;
  int tilewidth;
  std::string type;
std::string version;

}; */
int main(void) {
  JSON j;
  std::ifstream in("./assets/Map.json");
  in >> j;
  for (auto &el : j.items()) {
    std::cout << el.key() << " : " << el.value() << "\n";
  }
  return 0;
}

What are some smart ways of doing this?

CodePudding user response：

I prefer to provide a from_json function. It could look like this:

struct Configs final {
    int difficulty;
    int damage;
    bool infinite;
    int tilewidth;
    std::string type;
    std::string version;
};

void from_json(const json& j, Configs& c) {
    j.at("difficulty").get_to(c.difficulty);
    j.at("damage").get_to(c.damage);
    j.at("infinite").get_to(c.infinite);
    j.at("tilewidth").get_to(c.tilewidth);
    j.at("type").get_to(c.type);
    j.at("version").get_to(c.version);
}

You could then populate a Configs like this:

in >> j;
auto conf = j.get<Configs>();

CodePudding user response：

You're gonna have to dig into the documentation for your JSON library. Figure out how to check the types of each member you've parsed. Docs here recommend making a from_json function for your class/struct type. It looks like they provide some helpful macros for connecting JSON fields to your class/struct fields, like NLOHMANN_DEFINE_TYPE_NON_INSTRUSIVE

This seems to work alright

I'm assuming from_json is going to throw. Make sure you handle errors.

#include <string>
#include <nlohmann/json.hpp>
using namespace std::string_literals;

static const auto sampleJson = R"(
{
    "difficulty":-1,
    "damage":100,
    "infinite":true,
    "tilewidth":16,
    "type":"map",
    "version":"1.2.4"
}
)"s;

struct Configs final {
  int difficulty;
  int damage;
  bool infinite;
  int tilewidth;
  std::string type;
  std::string version;
};

NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(Configs, difficulty, damage, infinite, tilewidth, type, version);

using JSON = nlohmann::json;
int main(void) 
{
  try {
    auto j = JSON::parse(sampleJson);
    Configs c;
    from_json(j, c);
  }
  catch (...) {
      return 1;
  }

  return 0;
}